Loaded transmission line



Nov. 8, 1938. E. K. VAN TAssEL l 2,135,509

LOADED TRANSMISSION LINE Filed Aug. 27, 1956 /NVEA/rof? E ./f. M4N TASSEL BVM A 70m/,5y

Patented Nov. 8, 1938 A 135mg PATENTOFFICE 2,135,609 LOADED TRANsMissroN' LINE Earl Kenneth Van Tassel, GreatfKills, N. '.Y.,assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y.,'a corporation of -New York Application August 27, 1936; sen-a1 1-r0.19s,`1'11y v 6 Claims.

This invention relates to electricaltransmis- 'sionr lines landv particularly to means for loading'such lines,A l Y 'Y M It' is known that the transmission character- 135 istics of a; line may be improved by providing loadingI such as leakage paths between they conductors of the line at intervals along its length. The 'amount of leakage to be provided depends A upon the spacing of the paths, thev top frequency @T 'to bek transmitted, and the chosen compromise between perfect transmission and perfect -temperature correction. One method of providing these 'leakage-paths consists in inserting shunt resistances at 'the proper points along av-line.

Since'- these resistances are placed at' particular points along a line they are not affected by the samev temperature variationsas the remainder of the line and hence their compensating effects are not accurate.A This means that the trans- ?29 mission `loss at any given frequency cannot be accurately predicted and hence the signal might be distorted.

'I'he object of this invention is to provide improved loading for a transmission line.

#25 In its preferred form this invention comprises Aav loop-of. resistance wire connected across the line and distributed throughout the cable so that vit is subjected to the same temperature variations 'asthe cable itself. These loops may be '1.3.0 of any length, but it is preferred, thatfthey'be of the same length as a reel of cable. A transmissiony line incorporating thisv invention, therefore, may consist of pairs of wires connected together at each splicing of a reel and connect- 35 ed across the transmission pair at the opposite end of each reel.

In the drawing which accompanies this speciiication and forms a part thereof, Fig. 1 shows how the novel loading may be applied to a cable 40 and Fig. 2 shows an equivalent transmission network.

Referring now to Fig. 1, I0 is a pair of conductors forming a transmission line. This pair may be one of several hundred incorporated in 45 a single cable. Transmission pair I Il may be twisted to provide a certain amount of inductive loading as is customary in such construction. Since transmission lines are made up, in general, of a number of relatively small sec- 50 tions, i. e., of a number of reels, these sections 'fmust be spliced at intervals to form a continuous line. Two sections, I2 and I3, are shown vspliced to transmission pair I0 at I4 and l5 respectively. Within cable sheath Il is also in- 65 cluded a pair of resistance wires I 6, the resist- (c1. Y17a-45) ancre-temperature ,coeflicient of which is the saine as thaty of 'transmission pair I0. Resistyance pair I6Yis connected across transmission pair II'Iv atfthe cable splice I4 and the opposite end yI'l l is short-circuited.r Transmission pairs I2 and I3 likewise are shunted by resistance pairs I 8 and v,I 9" respectively.

Sincel the v"resistance wirey is distributed throughoutf'the' cable instead of being wound on the customary support and located approxi- 10 mately at yone point, it is subjected to exactly the same temperature variation as the transmission pair and hence temperature effects upon the transmission characteristics of the cable may be eliminated." This, however, lis predicated upon the assurntionr that a resistancey wire is available which has the correct 'resistance value for the length employed andat fthe same time has the same'resistance temperature coefficient as the transmission pair.' ,If sucha wire is not available, a compromise must be made. It 4will beV necessary to choose between a perfect transmission characteristic and a good temperature correction on one hand, and a perfect temperature correction and a nearly flat transmission characteristic'on' the other. It is of course possible to obtain compromises between these two extremes.- j f v 1 g f If desired, the resistance pairs may be incorporatedjina separate cable located adjacent the transmission line. l

The equivalent transmission network for the loaded cable-of Fig. 1 is'shown in Fig. 2. It may be considered as a balanced'line having series inductances 20 and resistances 2I and shunt re- 35 sistances 22 and capacitances 23. The resistance loading may be considered to be a similar network 24 shunted across the line at predetermined intervals. For a complete discussion of such networks reference may be made to K. S. John- 40 sons book entitled Transmission Circuits for Telephonie Communication, Van Nostrand Company, 1924. As an illustration of the application of this invention to a specific cable construction, a resistance of 105 ohms at 1 F. having the same temperature coeflicient as a 16 gauge pair commonly used for transmission, and shunted across such a pair at 18,000 foot intervals, will result in a practically constant transmission loss for frequencies from 0 to 8,000 cycles. In addition to this leveling effect upon the transmission loss, changes in the loss due to temperature changes in the medium surrounding the transmission pair and shunt will be materially reduced. If

it is desired to maintain the same transmission loss for frequencies above 8,000 cycles, it is necessary to increase the resistance of the shunt and decrease the distance between shunts. For example, spacings of 3,000 feet would result in maintaining a substantially constant loss for a frequency range of 0 to 60,000 cycles, and a still further reduction in spacing, such "as one .shunt of 3,850 ohms at 1 F. for each reel length,` i. e., about 500 feet, would extend the upper Vlimit to about 200,000 cycles. Y'

Thus from the design shown in Fig. v1it is a parent that the load resistances are inthe `same thermal medium as the transmission Vline and hence will follow very closelyY the temperature variations in the line. In 1addition Ito this desirable feature, the resistance pair will have a smooth impedance characteristic which may -ibe changed by altering the position of the Wires in the cable. A flatter frequency characteristic -Will result by making the impedance Aslightly inductive. This system of loading approaches very closely the dealcontinuous .loading and .resul-ts in cheaperlcable carrier .systems since smaller repeaters may kbe used. vIts applicability` is not limited to long lines for .message Aand broad band systems, but it may be fused for short local circuits designed for anyWide band transmission, and when vso used, greatly reduces phase-.distortion, the equalization necessary and the-effect ofv temperature on theoverall transmission.

It is understood that the foregoing description is merely illustrative of the invention and -that the scope of the invention is not to be determined thereby, .but by the appendedvclaims.

What is claimed is:

1. AV transmission :line comprising a cable, a

sheathing therefor, and shunt Aresistances WithinY the sheathing .for loading said line, said resistances comprising Wires which extend substantially the entire length of the cablefbetweenpointsof connection to the line.

2,. A transmission-system comprisinga plurality of reel lengths of cablejspliced togethezgfeach reel length of cable including a'reel length of -line and a `pair of resistance wires having substantial-ly the same resistance-temperature ycoefficient as the line, the Wires of said pair being connected together at one end of the .reel length of 'cablezand connected across the line at .the `@.Dllosite end of the reel length of cable to form ashuntresistance load whichiscoextensive with the reellength of line and subject :to thesame temperature variations as the reel llength of line.

Iand the specic resistivity and resistance-tem- Aspliced lengths of four-Wire lead, each Vlength comprising two parallel relatively high conductivity conductors and one pair of relatively low .conductivity yconductors permanently connected together at'oneend to form a loop conductor, the

A'temperature-conductivity characteristic of said loop adapted to provide loading for said parallel conductors, and the `said loop permanently connected across said parallel conductors so as to provide equally spaced loadsalong said transmissionline. Y Y n r5. VA Wide frequency :range transmission system comprising a plurality of spliced equivalentcable lengths each comprising a cable sheath enclosing one or :more transmission lines laid up :together with anV equal number of loops of resistance Wire coextensive With said 4transmission lines, the yends -of each of said resistance wire loops permanently connected `across its associated transmission -line peratures and of frequency, transmission of said 35( transmission line.

l6. A .transmission line comprisinga plurality of equal lengths of four conductor leads, one pair-of said leads of higher conductivity andspliced length to length to 'formthe `main channel .-o'f the splice :of the .high conductivity .pair there is i5 shunted the loop of the low conductivity pair, vand .the temperature resistance coeiiicient of fthe :10W

conductivity .loop substantially equivalent to the temperature resistance coefiicient rof the `high conductivity pair.

EARL VAN .TASSEL 

